Codegen: Add ref.is_invalid instruction

Spidermonkey returns a sentinel ref value of '-1' from some VM functions
to indicate failure. This commit adds an instruction analagous to ref.is_null
that checks for this value.

cranelift/codegen/meta/src/isa/x86/encodings.rs

@@ -2329,10 +2329,12 @@ fn define_reftypes(e: &mut PerCpuModeEncodings, shared_defs: &SharedDefinitions,
     let shared = &shared_defs.instructions;
 
     let is_null = shared.by_name("is_null");
+    let is_invalid = shared.by_name("is_invalid");
     let null = shared.by_name("null");
     let safepoint = shared.by_name("safepoint");
 
     let rec_is_zero = r.template("is_zero");
+    let rec_is_invalid = r.template("is_invalid");
     let rec_pu_id_ref = r.template("pu_id_ref");
     let rec_safepoint = r.recipe("safepoint");
 
@@ -2345,6 +2347,9 @@ fn define_reftypes(e: &mut PerCpuModeEncodings, shared_defs: &SharedDefinitions,
     // is_null, implemented by testing whether the value is 0.
     e.enc_r32_r64_rex_only(is_null, rec_is_zero.opcodes(&TEST_REG));
 
+    // is_invalid, implemented by testing whether the value is -1.
+    e.enc_r32_r64_rex_only(is_invalid, rec_is_invalid.opcodes(&CMP_IMM8).rrr(7));
+
     // safepoint instruction calls sink, no actual encoding.
     e.enc32_rec(safepoint, rec_safepoint, 0);
     e.enc64_rec(safepoint, rec_safepoint, 0);

cranelift/codegen/meta/src/isa/x86/recipes.rs

@@ -3222,6 +3222,26 @@ pub(crate) fn define<'shared>(
             ),
     );
 
+    recipes.add_template_recipe(
+        EncodingRecipeBuilder::new("is_invalid", &formats.unary, 2 + 3)
+            .operands_in(vec![gpr])
+            .operands_out(vec![abcd])
+            .emit(
+                r#"
+                    // Comparison instruction.
+                    {{PUT_OP}}(bits, rex1(in_reg0), sink);
+                    modrm_r_bits(in_reg0, bits, sink);
+                    sink.put1(0xff);
+                    // `setCC` instruction, no REX.
+                    use crate::ir::condcodes::IntCC::*;
+                    let setcc = 0x90 | icc2opc(Equal);
+                    sink.put1(0x0f);
+                    sink.put1(setcc as u8);
+                    modrm_rr(out_reg0, 0, sink);
+                "#,
+            ),
+    );
+
     recipes.add_recipe(
         EncodingRecipeBuilder::new("safepoint", &formats.multiary, 0).emit(
             r#"

cranelift/codegen/meta/src/shared/instructions.rs

@@ -3190,6 +3190,24 @@ pub(crate) fn define(
         .operands_out(vec![a]),
     );
 
+    let a = &Operand::new("a", b1);
+    let x = &Operand::new("x", Ref);
+
+    ig.push(
+        Inst::new(
+            "is_invalid",
+            r#"
+        Reference verification.
+
+        The condition code determines if the reference type in question is
+        invalid or not.
+        "#,
+            &formats.unary,
+        )
+        .operands_in(vec![x])
+        .operands_out(vec![a]),
+    );
+
     let Cond = &Operand::new("Cond", &imm.intcc);
     let f = &Operand::new("f", iflags);
     let a = &Operand::new("a", b1);